This invention relates to apparatus for the doping of a semiconductor rod held inside a crucible free float-zone apparatus, and it relates, more particularly, to the introduction of dopant pellets into the localized float-zone, (produced in the semiconductor rod by an induction heating coil), with at least one hopper for introducing the dopant pellets, provided with an exit port, and with an outlet conduit connected to the exit port and directed at the float zone.
Typical conventional apparatus of this kind has been described in U.S. Pat. No. 4,270,972. The hopper for holding the dopant pellets is located external to the float-zone apparatus. The outlet conduit passes through the wall of the float-zone apparatus into the interior. Since zone melting is conducted either in a vacuum or in a protective gas, the hopper, arranged on the outside of the float-zone apparatus, must be vacuum tight and/or gas tight. The evacuation of the hopper, which must also take place prior to zone melting in a protective gas can of course, take place through the outlet conduit, but this is very inefficient due to the small cross-section of the outlet conduit. An additional exhaust tube, or larger cross-section, to the magazone would further complicate the apparatus.